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Find the area of a triangle two sides of which are 18cm and 10cm and the perimeter is 42cm.

Posted by Janvi Shevate 5 years, 6 months ago

CBSE > Class 09 > Mathematics

3 answers

Rakhi Vasodiya11 5 years, 6 months ago

√(21-18)(21-10)(21-14) √ 3 × 11 × 7 √231 cm sq.

1Thank You

Rakhi Vasodiya11 5 years, 6 months ago

Perimeter = sum of all sides of triangle i.e. 42 = 18+10+c 42 = 28+c 42-28=c 14=c Then, semi - perimeter = a+b+c/2 = 18+10+14/2 = 42/2 = 21 cm. Now, you can easily find area using heron's formula

1Thank You

Yogita Ingle 5 years, 6 months ago

Given,
Side a=18cm
Side b=10cm
Perimeter=42cm=a+b+c
:. Putting value
42=18+10+c
42=28+c
42-28=c
14=c
Now,
S=(a+b+c)/2
:. Putting value
S=42/2
S=21
Now according to Heron's formula-
Area of a triangle
=√{s(s-a)(s-b)(s-c)}
:. Putting value
=√{21(21-18)(21-10)(21-14)}
=√{21(3)(11)(7)}
=√4851
=21√11cm²

1Thank You

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